1. Field of the Invention
This invention relates to an apparatus for transmitting a wide-screen TV signal, while keeping, the compatibility with an existing TV standard, and for receiving and displaying the wide-screen TV signal with fixed-rate horizontal scanning lines.
2. Description of the Prior Art
More than 37 years have passed since the color television broadcasting of the current NTSC (National Television System Committee) system was introduced in 1954 in the United States. In Europe, they have used the PAL (Phase Alternative Line) system since 1967. Recently, in search of a finer definition and higher performance television system, several new systems including the HDTV (High Definition Television) system have been proposed. At the same time, the contents of the programs presented to viewers have been changed from the mere studio programs to programs providing higher quality images and more realistic feeling such as cinema-size movies.
The current NTSC broadcasting is standardized by 2:1 interlaced 525 scanning lines, a luminance signal bandwidth of 4.2 MHz, and an aspect ratio of 4:3. (See, for example, Pritchard, "US Color Television Fundamentals -A Review", IEEE Trans. Consumer Electron., vol. CE-23, pp. 467-478, November 1977.) The current PAL broadcasting is standardized by 2:1 interlaced 625 scanning lines, a luminance signal bandwidth of 5.0 MHz in Germany, or 5.5 MHz in the U.K., and an aspect ratio of 4:3.
In this background, several television signal composition methods aiming at compatibility with the current broadcasting system and enhancement of horizontal and vertical resolution have been proposed. One such example is presented in a paper of Faroudja and Roisen, "Improving NTSC to achieve near-RBG performance", SMPTE J., vol. 96, pp. 750-761, August 1987. They use a comb filter to split luminance and chrominance signals at the transmitting end and avoid crosstalk between them at a receiver. This method is useful for eliminating an annoying crosstalk on the received image, but horizontal and vertical high frequency components of the luminance signal cannot be transmitted, nor can an enhancement of the resolution be attained.
Another example is presented in a paper of Fukinuki and Hirano, "Extended Definition TV Fully Compatible with existing Standards", IEEE Trans. Commun., vol. COM-32, pp. 948-953, Aug. 1984. Considering the NTSC television signal expressed on a two-dimensional plane of temporal frequency f1 and vertical frequency f2, chrominance signals C are present in the second and fourth quadrants due to their phase relationship to the chrominance subcarrier fsc. The Fukinuki et al example uses the vacant first and third quadrants for multiplexing the high frequency components of the luminance signal. These vacant quadrants are called the "Fukinuki Hole" after the inventor. The chrominance signal and the multiplex high frequency components are separated and reproduced at the receiving end, thereby enhancing the horizontal resolution. In this example, the conventional NTSC receiver would be interfered with by the multiplex signal, because the example has no ability for separating the chrominance signal from the multiplex high frequency components.
In the current television broadcast, as is clear from the description above, the signal bandwidth is limited by the standard, and it is not easy to add some new information with a high quality. For example, other methods to enhance the horizontal resolution have been proposed (M. Isnardi et al, "A Single Channel NTSC Compatible Widescreen EDTV System", HDTV Colloquium in Ottawa, October, 1987), but many problems are left unsolved from the viewpoint of the compatibility with the current television broadcasting and the deterioration of demodulation characteristics of the high frequency components in a moving picture. Besides, from the standpoint of effective use of the frequency resources, the transmission band cannot be easily extended.
We invented a method of superposing a signal by using quadrature modulation of the video carrier (see U.S. Pat. No. 4,882,614 issued Nov. 21, 1989, or see Yasumoto et al, "An extended definition television system using quadrature modulation of the video carrier with inverse Nyquist filter", IEEE Trans. Consumer Electron., vol. CE-33, pp. 173-180, August 1987). By this method, various signals can be transmitted using a newly established quadrature channel and the interference to the conventional NTSC receiver is very small in principle. But the interference can be detected in practice, because of the incompleteness of the characteristics of the filters used by the receiver and the transmitter.
We also reported transmitting wide-screen images which are compatible with the conventional standard, using quadrature modulation of the video carrier. (See. Yasumoto et al, "A Wide aspect ratio television system with full NTSC compatibility," IEEE Trans. on Consumer Electronics. Vol CE-34, No. 1. February, 1988.) In this paper we described transmitting side panels which are left and right parts of a wide-screen image after separating the side panels and the center panel(4:3 portion), and re-composing them at the receiving side. This method of transmitting wide-screen images by splitting the side panels and the center panel is called the "side panel method".
Another method to transmit wide-screen images which are compatible with the existing standard is called the "letter box method". In this method, one can see a 16:9 wide-screen image even with the conventional receiver although black bars appear both on the upper and lower parts of the image. Using these black parts, we can transmit additional signals for enhancing the horizontal and vertical resolution. One example using this method is described in the Lippman et al paper entitled: "Single-channel backward-compatible EDTV systems", SMPTE Journal, Vol. 98, No. 1, January, 1989.
There are some advantages and disadvantages both in the side panel method and the letter box method. The disadvantage with the side panel method is the stitching of the side panels and the center panel. During severe receiving conditions, just as with weak electric or multi-path fields, it is easy to detect the differences between the panels due to noise or ghosts. One of the other disadvantages with the side panel method is the difficulties in selecting the center panel out of the wide-screen image. There arises a problem if an important object disappears in the center panel on the conventional receiver. It is also difficult to select the center panel out of the wide-screen image according to the desire of the director at the transmitting side.
The disadvantage with letter box method is the difficulties to find a channel for transmitting the high frequency component of the luminance signal in order to compensate for the loss of the vertical resolution of the original image. One possibility is to transmit it in the black bars. It is still a problem to reconstruct the original image with a full vertical resolution at the receiving side. All examples of the letter box method so far adopt 360 lines out of 480 lines with the NTSC standard, and recover 480 lines at the receiving side. The conversion from 360 lines to 480 lines (3 to 4) consumes a large amount of circuits and line memories.
This invention relates to how to reconstruct the original image at the receiving side with a simple circuit, using the letter box method.